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Finding Truth in DNA Mixture Evidence
Innocence Network ConferenceInnocence Network ConferenceApril, 2013April, 2013
Charlotte, NCCharlotte, NC
Mark W Perlin, PhD, MD, PhD Mark W Perlin, PhD, MD, PhD Cybergenetics, Pittsburgh, PACybergenetics, Pittsburgh, PA
Cybergenetics © 2003-2013Cybergenetics © 2003-2013
DNA Mixture DataQuantitative peak heights at a locus
peak size
peakheight
Peak Thresholds
Threshold
Under threshold, don't use alleles
Allele Pair7, 77, 107, 127, 14
10, 100%10, 12
10, 1412, 1212, 1414, 14
Simplify data for human review
Allele Dropout
Threshold
Under threshold, use alleles anyway
Allele Pair7, 77, 107, 127, 14
10, 10> 0% 10, 12
10, 1412, 1212, 1414, 14
Conjure phantom peaks
Human Interpretation Issues
Evidence• call good data inconclusive• peaks are too low for them• too many contributors to handle• potential examination bias
Database• hit by association, not by match• comparison: make false hits• restrict upload: lose true hits
TrueAllele® Casework
Evidence• preserve data information• use all peaks, high or low• any number of contributors• entirely objective, no bias
Database• hit based on LR match statistic• sensitive: find true hits• specific: only true hits
Validation Studies
Perlin MW, Sinelnikov A. An information gap in DNA evidence interpretation. PLoS ONE. 2009;4(12):e8327.
Perlin MW, Legler MM, Spencer CE, Smith JL, Allan WP, Belrose JL, Duceman BW. Validating TrueAllele® DNA mixture interpretation. Journal of Forensic Sciences. 2011;56(6):1430-47.
Perlin MW, Belrose JL, Duceman BW. New York State TrueAllele® Casework validation study. Journal of Forensic Sciences. 2013;58(6):in press.
Separate Mixture Contributors
25% 75%
GenotypeThorough: consider every possible genotype solutionObjective: does not know the comparison genotype
Explain thepeak pattern
Betterexplanationhas ahigher likelihood
Victim's allele pair
Another person's Another person's allele pairallele pair
Allele Pair7, 77, 107, 127, 14
10, 1098%10, 12
10, 1412, 1212, 1414, 14
Handgun @ locus TH01Three person mixtureLab says: inconclusive
TrueAllele mixture interpretationGenotype probability distributionThorough & objective
Handgun does NOT match suspectComputer statistic AGAINST match
Informative TrueAllele genotypeExpected match statistic: million/billionSearch a DNA database for the right man?
The Search for Truth
M. W. Perlin, "When good DNA goes bad," Journal of Forensic Research, S11:003, 2013.
M. W. Perlin, "DNA Identification Science," in Forensic Sciences, volume 3. C. H. Wecht, Ed., Albany, NY: LexisNexis Matthew Bender, Chapter 37C, 2012.
M. W. Perlin. "Forensic science in the information age." Forensic Magazine, 9(2):17-21, 2012.
More information
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